Project: Gimme

Publisher: Searls

argument matchers

By default, gimme will only stub and verify methods that are called with the same arguments
in your spec and your production code. But gimme also includes a number of argument matchers
that allow more flexible specifications, particularly when you don't care about or can't
know the exact arguments passed to a method on a test double.

This example illustrates:

How to use an argument matcher when stubbing a method

Using argument matchers when verifying a method

Using argument captors, a special sort of matcher

Defining your own matcher

In this example, we have a Mail object with a contents attribute. A DeliversMessages object adds Mail to
Recipients' mailboxes and checks off each delivery on its Checklist.

Background

Given

we have this existing code:

class Mail
  attr_reader :contents
  def initialize(contents)
    @contents = contents
  end
end

class Recipient
  def add_to_mailbox(thing)
  end
end

class Checklist
  def check_off(message_summary, recipient, timestamp)
  end
end

class DeliversMessages
  def initialize(checklist = Checklist.new)
    @checklist = checklist
  end
end

When

we want to write some tests to help us write this method:

class DeliversMessages
  def deliver(message, recipient = Recipient.new)
    mail = Mail.new(message)
    recipient.add_to_mailbox(mail)
    @checklist.check_off(message[0..4], recipient, Time.now)
  end
end

Scenarios

stubbing with argument matchers
using some built-in matchers
using an argument captor to grab what was passed
writing a custom starts_with matcher

stubbing with argument matchers

Then

we can use gimme to isolate the unit under test:

# pretend we want to ensure the #deliver function returns
#   whatever the Checlist#check_off method returns. We can
#   specify that by stubbing the check_off method
checklist = gimme(Checklist)
recipient = gimme(Recipient)
give(checklist).check_off(anything, anything, is_a(Time)) { "Pandas!" }

result = DeliversMessages.new(checklist).deliver("WHY HELLO GOOD SIR", recipient)

result.should == "Pandas!"

using some built-in matchers

Then

we can use gimme to isolate the unit under test:

checklist = gimme(Checklist)
recipient = gimme(Recipient)

DeliversMessages.new(checklist).deliver("WHY HELLO GOOD SIR", recipient)

verify(recipient).add_to_mailbox(is_a(Mail))  #would force a Mail instance
verify(recipient).add_to_mailbox(any(Mail))   #would also have allowed nil

verify(checklist).check_off(any(String), recipient, anything) #anything matches anything

using an argument captor to grab what was passed

Then

we can use gimme to isolate the unit under test:

checklist = gimme(Checklist)
recipient = gimme(Recipient)

DeliversMessages.new(checklist).deliver("WHY HELLO GOOD SIR", recipient)

mail_captor = Gimme::Captor.new
verify(recipient).add_to_mailbox(capture(mail_captor))
mail_captor.value.contents.should == "WHY HELLO GOOD SIR"

writing a custom starts_with matcher

Then

we can use gimme to isolate the unit under test:

checklist = gimme(Checklist)
recipient = gimme(Recipient)

DeliversMessages.new(checklist).deliver("WHY HELLO GOOD SIR", recipient)

class StartsWith
  def initialize(expected)
    @expected = expected
  end

  def matches?(actual)
    actual.start_with?(@expected)
  end
end
def starts_with(s)
  StartsWith.new(s)
end

verify(checklist).check_off(starts_with("WHY"), anything, anything)

Last published about 7 years ago by searls.

argument matchers

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